The present invention discloses an improved probe structure, which is installed in the body of an infrared clinical thermometer and comprises a plastic hollow casing having an opening; a curved block annularly arranged inside the opening; a hollow sleeve arranged inside the casing and along the perimeter of the opening; a temperature sensor arranged inside sleeve and below the curved block; a support element arranged inside the sleeve and supporting the temperature sensor; and a thermal insulation ring encircling the temperature sensor and pressing against the inner wall of the sleeve. The thermal insulation ring has an outer diameter larger than a width of the temperature sensor, and an air gap is thus formed between the temperature sensor and the inner wall of the sleeve; the top of the thermal insulation ring has an altitude higher than the top of the temperature sensor, and another air gap is thus formed between the temperature sensor and the curved block. Thereby is effectively retarded heat conduction from the external to the temperature sensor.